Interpretive Summary:
Nematode pathogens which infect the abomasum of ruminant hosts continue to represent a major health challenge for both domestic and free ranging ungulates in North America and globally. Such nematodes, and particularly the medium stomach worms (referred to as the subfamily Ostertagiinae), represent a substantial economic threat due the costs of disease and treatment to control infections. Although we have considerable information about these parasites in domestic ungulates, there remains much that is unknown about species diversity, host associations (and patterns of exchange between domestic and wild ungulates) and geographic range. Further globalization of agriculture has continued to influence the overall distributions for these pathogens due to translocation and introduction of infected hosts. Although the global fauna and its intricate structure of endemic and introduced species in most biogeographic regions is becoming understood, previously unrecognized genera and species continue to be discovered, particularly in Africa. One third of known genera of ostertagiines are endemic to Africa, yet comprehensive surveys for many species of ungulates have not been conducted and parasitological examinations have often been based on relatively few hosts or have focused on relatively restricted geographic zones. Based on surveys of parasite faunas in Africa, we now establish and describe a new genus and species of medium stomach worm, Robustostrongylus aferensis, in African ungulates. Our research contributes to an accurate definition of diversity, including reliable taxonomy, which in conjunction with comprehensive data for host and geographic distributions are the cornerstones for understanding epizootiolgy and patterns of emerging disease across a mosaic of rapidly changing environments and for development of efficient and robust measures for control of parasitism in ungulates.

Technical Abstract:
Abomasal nematodes (Ostertagiinae: Trichostrongyloidea) representing a previously unrecognized genus and species were discovered in kob, Kobus kob and Kongoni (Hartebeest), Alcelaphus buselaphus jacksonii from Uganda during surveys of ungulate parasites in the 1960’s. Robustostrongylus aferensis gen. nov. et sp. nov. is characterized by a ventriculus-like bilobed valve at the junction of the esophagus and intestine, a synlophe with unusually robust ridges, cervical papillae and excretory pore situated posterior to the mid-length of the esophagus, a unique body form and large diameter in males and females, and a relatively anterior position for the vulva, and strongly convoluted and spiraled ovarian tracks in females. Bursal structure is 2-1-2, with subequal Rays 2/3, strongly reduced and robust Rays 8, and relatively narrow Rays 9/10 contained within a reduced, laterally inflated dorsal lobe. Spicules are filamentous and tripartite; the gubernaculum is cryptic, alate and heart shaped in the anterior. Robustostrongylus aferensis, with narrow filamentous spicules that trifurcate distally near 80%, paired arcuate “0” papillae that terminate in bulbous expansions, and a reduced dorsal lobe and ray most closely resembles species of Longistrongylus. A suite of unique characters, consistent in males and females, however, unequivocally distinguishes specimens of Robustostrongylus aferensis from all ostertagiines with either a 2-1-2 or 2-2-1 bursal pattern. Among 15 genera of the Ostertagiinae in the global fauna, 5 are entirely limited in distribution to Africa, including Africanastrongylus, Hamulonema, Longistrongylus, Pseudomarshallagia, and Robustostrongylus gen. nov.; species among 5 additional genera including Cervicaprastrongylus, Hyostrongylus, Marshallagia, Ostertagia and Teladorsagia also occur in Africa but are represented as mosaics, with diversity centered in Eurasia or the Holarctic.